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When we use pack bitmaps rather than walking the object graph, we end up with the list of objects to include in the packfile, but we do not know the path at which any tree or blob objects would be found. In a recently packed repository, this is fine. A fetch would use the paths only as a heuristic in the delta compression phase, and a fully packed repository should not need to do much delta compression. As time passes, though, we may acquire more objects on top of our large bitmapped pack. If clients fetch frequently, then they never even look at the bitmapped history, and all works as usual. However, a client who has not fetched since the last bitmap repack will have "have" tips in the bitmapped history, but "want" newer objects. The bitmaps themselves degrade gracefully in this circumstance. We manually walk the more recent bits of history, and then use bitmaps when we hit them. But we would also like to perform delta compression between the newer objects and the bitmapped objects (both to delta against what we know the user already has, but also between "new" and "old" objects that the user is fetching). The lack of pathnames makes our delta heuristics much less effective. This patch adds an optional cache of the 32-bit name_hash values to the end of the bitmap file. If present, a reader can use it to match bitmapped and non-bitmapped names during delta compression. Here are perf results for p5310: Test origin/master HEAD^ HEAD ------------------------------------------------------------------------------------------------- 5310.2: repack to disk 36.81(37.82+1.43) 47.70(48.74+1.41) +29.6% 47.75(48.70+1.51) +29.7% 5310.3: simulated clone 30.78(29.70+2.14) 1.08(0.97+0.10) -96.5% 1.07(0.94+0.12) -96.5% 5310.4: simulated fetch 3.16(6.10+0.08) 3.54(10.65+0.06) +12.0% 1.70(3.07+0.06) -46.2% 5310.6: partial bitmap 36.76(43.19+1.81) 6.71(11.25+0.76) -81.7% 4.08(6.26+0.46) -88.9% You can see that the time spent on an incremental fetch goes down, as our delta heuristics are able to do their work. And we save time on the partial bitmap clone for the same reason. Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Git - the stupid content tracker
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"git" can mean anything, depending on your mood.
- random three-letter combination that is pronounceable, and not
actually used by any common UNIX command. The fact that it is a
mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the
dictionary of slang.
- "global information tracker": you're in a good mood, and it actually
works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks
Git is a fast, scalable, distributed revision control system with an
unusually rich command set that provides both high-level operations
and full access to internals.
Git is an Open Source project covered by the GNU General Public
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Please read the file INSTALL for installation instructions.
See Documentation/gittutorial.txt to get started, then see
Documentation/everyday.txt for a useful minimum set of commands, and
Documentation/git-commandname.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with "man gittutorial" or "git help tutorial", and the
documentation of each command with "man git-commandname" or "git help
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CVS users may also want to read Documentation/gitcvs-migration.txt
("man gitcvs-migration" or "git help cvs-migration" if git is
installed).
Many Git online resources are accessible from http://git-scm.com/
including full documentation and Git related tools.
The user discussion and development of Git take place on the Git
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The maintainer frequently sends the "What's cooking" reports that
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